The present invention relates to an axial blower used for a blower of an outdoor unit of an air conditioner or the like.
One example of a conventional axial blower of this type is shown in, for example, FIG. 10. This axial blower 1 is provided with a plurality of vanes 3 formed integrally around a central hub 2 equidistantly in the circumferential direction thereof.
With reference to FIGS. 10-12, the cross-sectional shape of each vane 3 in the circumferential direction A-B at a portion having a radially arbitrary distance D from the center O of the hub 2 is formed into a thick stream-line shape 3d from the negative pressure surface-side leading edge portion 3a of the vane 3 to a vane surface 3c as shown in FIG. 11.
The thick shape 3d advantageously allows an air flow F flowing from the negative pressure surface-side leading edge portion 3a of the vane 3 to travel along the positive and negative pressure sides of the vane surface 3c as indicated by arrows shown in FIG. 12, prevents the air flow F from separating from the vane surface 3c and makes small a trailing vortex Vf formed in the back of a vane trailing edge portion 3b thereby to reduce a blowing sound.
When the conventional axial blower 1 as mentioned above is incorporated, as a blower, into the outdoor unit of an air conditioner to increase the number of revolution of the blower per unit time (to be simply referred to as "the number of revolution" hereinafter) and to increase the quantity of blast, following disadvantages occur. That is, static pressure in the outdoor unit rises, the inflow angle of the air flow F with respect to the negative pressure surface-side leading edge portion 3a of each vane 3 varies and the separation of the air flow tends to occur on the vane surface 3c, thus increasing the blowing sound.
Further, it is easily be understood that the term "negative pressure side" used herein means an air-sucking side and the term "positive pressure side" used herein means an air-blowing side with respect to the vanes of the axial blower.